Purification of 2-body DMs

Thanks for the nice code.

We've been playing around a bit with implementing some algorithms to purify a given 2-body reduced density matrices to make them (approximately) N-representable, initially based on the work of https://doi.org/10.1063/1.4994618 that I know some of the PyCI developers were involved in.

I'm aware that related algorithms for this purpose are an undocumented feature of the PyCI code, and was wondering whether they are a) functionally complete [the P and Q conditions don't seem to be implemented? We would be happy to add them], b) whether you are happy for them to be used, c) whether you can provide a simple example to be sure that we are using the code correctly or any caveats you want to mention on its limitations or effective use?

Many thanks,
George

No source files or tests are named. Start by locating PyCI's undocumented 2-body reduced density matrix purification algorithms, then inspect whether the P and Q conditions are implemented and how the existing routines are called. Done means clarifying functional completeness, providing a simple usage example, and documenting relevant limitations or caveats.